The object of separating different materials which constitute a conveyed flow of material, arises in various applications, such as in the purification of wood material and particularly in the separation of heavy materials from shredded commercial waste, industrial waste, domestic waste etc.
Magnetic separators can be used for iron-containing metal materials, which, however, are useless for sorting non-metallic heavy materials, such as stones, ceramic material or glass.
So-called air separators for classifying and sorting the components of a flow of material are very popular. In these machines the flow of material is conveyed into an inspection chamber and is exposed to a conveying air flow. The flow of material is for instance (see German laying-open specification DE 199 45 646 A1) conducted into a drum by means of a transport device and while the drum rotates, a flow of air guided through the drum conducts material components of a low specific density in the direction towards a drum outlet arranged on a higher level, which is possibly connected to a vacuum chamber, to discharge the material components, while heavier material components are merely entrained by the drum to be discharged at a drum outlet arranged on a lower level. At the transition from the upper drum outlet to the outlet channel, a controllable air barrier can also be provided to further improve the sorting process.
In other embodiments of air separators, lighter materials can be transported via an air bridge between two transport devices, said air bridge being generated by a fan, while heavy materials fall through between the transport devices. Such a pure air separation particularly involves the disadvantage of the required frequent adjustment of the air flow depending on the material composition. The required air quantity is very high and the separation accuracy is significantly restricted, as is the case in the above-mentioned method.
A combination of the air bridge alternative with a mechanical intermediate conveyance through a roller rotating in the general conveying direction, to which light substances are conveyed by an upstream transport device by means of a fan acting from below, whereas heavy materials shall fall into the gap between this transport device and the roller, also has the disadvantage of a higher quantity of air required. Thus, these embodiments are particularly susceptible to moisture. Furthermore, adhesive heavy materials reaching the drum are disadvantageously conveyed through the drum to the downstream transport device.
Besides pure or combined air separators, purely mechanical sorting apparatus also exist. The flow of material is for instance introduced through a transport device from the top into the contact area between two brush rollers rotating in opposite direction towards the outside. Lighter materials shall follow the rotary movement of the roller, whereas heavy materials shall be conducted through the contact area between the rollers. Besides the problem of winding up thin expanded materials, it is unavoidable in such a design that along with the heavy materials that are sorted out by the brush bristles in the contact area, light, particularly relatively small light material components, disappear from the flow of material.
Thus, it is the object of the present invention to provide an improved heavy material separator and to provide a method of separating heavy materials from an inhomogeneous flow of material whose reliability in the prior art is not affected or only to a small extent by the above-mentioned problems.